摘要:

AbstractThe somatomedins are potent stimulators of proliferation and differentiation of cultured myoblasts. In studies on the mechanism(s) of these actions, we have measured the activities of ornithine decarboxylase (ODC), an enzyme associated with rapid cell proliferation, and creatine kinase (CK), a biochemical marker for muscle differentiation, after treatment of L6 myoblast cultures with Multiplication Stimulating Activity (MSA), a member of the somatomedin family of insulinlike growth factors. ODC levels reached a peak 24 hours after MSA addition (before any detectable differentiation of the myoblasts) and then decreased as differentiation commenced and CK activity increased. Addition of alpha‐difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, caused a dramatic decrease in differentiation. Measurement of3H‐thymidine incorporation, DNA content, and cell number established that the effect of DFMO on differentiation was not a simple consequence of its antiproliferative actions. Cellular levels of putrescine and spermidine (but not spermine) decreased substantially following addition of DFMO to the cultures. The inhibitory effects of DFMO were abolished upon addition of exogenous polyamines to the medium. However, addition of polyamines in the absence of MSA or DFMO did not mimic the stimulation of differentiation by MSA. We conclude that polyamines play an essential role in the stimulation of L6 myoblast differentiation by somatomedins, but they are not sufficient to effect this stimulat

ISSN:0021-9541    

DOI:10.1002/jcp.1041200302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractVerapamil, a clinically important calcium channel blocker, has been found to cause a 40‐fold enhancement of killing of the human KB cell line by a cytotoxic conjugate of epidermal growth factor withPseudomonasexotoxin (EGF‐PE). Synergistic effects of verapamil and EGF‐PE are also seen on HeLa D98 cells and a human epidermal carcinoma cell line, A431. Verapamil also potentiates the effect of a toxic conjugate formed betweenPseudomonasexotoxin and a monoclonal antibody to the human transferrin receptor (anti‐TFR‐PE) and enhances the effect ofPseudomonasexotoxin (PE) alone. Two other calcium antagonists were tested. Diltiazem enhances the cytotoxic effect of EGF‐PE, but nifedipine does not. Verapamil does not affect the binding and uptake of125I‐EGF by KB cells, but it significantly delays the disappearance of internalized125I‐EGF from the cells. Density gradient fractionation studies using cell homogenates suggest that125I‐EGF accumulates in an undegraded form in lysosomes when cells are treated with verapamil. By immunofluorescence microscopy using an antibody to PE, EGF‐PE was found to accumulate in lysosomes; by electron microscopy the lysosomes had an abnormal appearance. The effects of verapamil on toxicity of EGF‐PE and lysosomal function appear to be related. However, it is not known whether the enhanced toxicity of EGF‐PE in the presence of verapamil is due to its delayed degradation in lysosomes or some more general effect of verapamil o

ISSN:0021-9541    

DOI:10.1002/jcp.1041200303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThrombospondin (TS), a 450,000 molecular weight glycoprotein, is released from α‐granules of thrombin‐activated platelets and is secreted and incorporated into the extracellular matrix by several cell types in culture. We have examined the effects of cell density and transformation on the production of TS in cell culture. The levels of TS, per cell, in the culture medium of endothelial cells, smooth muscle cells, and fibroblasts were greater at lower cell densities; in fibroblasts the levels of two other extracellular matrix proteins, fibronectin and collagen, were unaffected by cell density. Our evidence indicates that the higher levels of TS in the culture medium, determined for lower‐density cells, were achieved by an increased secretion of the protein rather than by a reduction in degradation or incorporation into the extracellular matrix. TS production by normal and transformed Wl‐38 fibroblasts was the same, although the fibronectin level in the culture medium of the transformed cells was substantially decreased. These findings suggest that the production of TS by cells in culture is regulated in a different fashion from that of fibronectin or

ISSN:0021-9541    

DOI:10.1002/jcp.1041200304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractStimulation of amiloride‐sensitive sodium (Na+) influx and the subsequent activation of NA+, K+‐ATPase by serum or growth factors have been implicated as early events leading to initiation of cell proliferation. We recently demonstrated that amiloride inhibits thrombin‐initiated DNA synthesis not by inhibiting an early event occurring during the first 8 hr, but rather by inhibiting some later event 8 to 12 hr after thrombin addition. To further probe the relationship between stimulation of ion influx and initiation of cell proliferation, human α‐thrombin was converted to γ‐thrombin, nitro‐α‐thrombin, and diisopropylphospho (DIP)‐α‐thrombin. These derivatives retain either the capacity to bind cell surface α‐thrombin receptors or thrombin esterase activity, but they do not initiate DNA synthesis. At low concentrations of α‐thrombin or the various thrombin derivatives, only α‐thrombin stimulates86Rb+influx, suggesting a correlation between stimulation of influx and the ability of these derivatives to initiate DNA synthesis. Concentrations of a DIP‐α‐thrombin that saturate the α‐thrombin recptors (up to 2 μg/ml) do not stimulate either the early or late influx of86Rb+, indicating that DIP‐α‐thrombin binding alone is not sufficient to stimulate ion fluxes. High concentrations of either γ‐thrombin or nitro‐α‐thrombin, however, stimulate both early and late86RB+uptake but do not initiate DNA synthesis. These results demonstrate that events leading to both the early and late stimulation of86Rb+influx by themselves are not sufficient to initiate cell proliferation. Thus, initiation may require a combination of events that can be indepe

ISSN:0021-9541    

DOI:10.1002/jcp.1041200305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe metabolism of the receptor for epidermal growth factor (EGF) in A‐431 cells has been measured by labeling the receptor in vivo with radioactive amino acid precursors and then determining, by immunoprecipitation with specific anti‐EGF receptor antisera, the rate of degradation of the receptor when the cells are placed in a nonradioactive medium. The rate of EGF receptor degradation (t½12= 20 hr) was faster than the rate of degradation of total cell protein (t½12= 52 hr). When EGF was added at the beginning of the chase, the half‐life of prelabeled receptor decreased to 8.9 hr. This decrease was specific, as the level of total cellular protein and another plasma membrane protein, the transferrin receptor, were relatively unaffected by EGF. The carbohydrate portion of the receptor is degraded, in the presence or absence of EGF, at approximately the same rate as the protein moiety. The amount of EGF receptor protein in A‐431 cells has been quantitated by radiolabeling total cellular protein and quantitating the immunoprecipitable receptor. The EGF receptor constitutes approximately 0.15% of the total cell protein in A‐431 cells. These cells, therefore, have approximately 30 times more EGF receptor protein than fibroblasts. The EGF receptor constitutes an even higher proportion of3H‐glucosamine‐ or3H‐mannose‐labeled macromolecules in A‐431 cells, 1.5% or 5.2%, respectively. The EGF receptor from A‐431 cells can easily be identified by submitting carbohydrate‐labeled, solubilized cells to electrophoresis as de

ISSN:0021-9541    

DOI:10.1002/jcp.1041200306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractCystamine together with colchicine markedly enhanced the uptake of [3H]‐thymidine into DNA of quiescent cultures of insulin‐stimulated Swiss 3T3 mouse fibroblasts. Flow cytofluorometric analyses showed an increased rate of transition of cells from G0/G1→ S + G2in response to combinations of insulin, colchicine, and cystamine. Cystamine, the most effective of several thiol compounds, gave maximal augmentation at 200 μM and was toxic at 300–500 μM. Amplification of DNA synthesis by cystamine was also obtained with epidermal growth factor, vasopressin, and 0.5% fetal bovine serum. Combinations of cystamine and other microtubule‐disrupting agents such as nocodazole, maytansine, and podophyllotoxin enhanced DNA synthesis in insulin‐stimulated cells. In experiments involving sequential addition of agents, significant enhancement of DNA synthesis was observed when the addition of colchicine to cystamine‐treated cells was delayed or conversely when the addition of cystamine to colchicine‐treated cultures was delayed. This reciprocal interaction between cystamine and colchicine suggests that a prereplicative intermediate accumulates in response to the action of these dissimilar compounds. We consider the possibility that cystamine may act by forming mixed disulfides with thiol groups of unknown protein(s) that regulat

ISSN:0021-9541    

DOI:10.1002/jcp.1041200307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractPrevious studies indicate that although normal and Simian virus (SV40)‐transformed WI38 human fibroblasts have similar levels of intracellular Ca++on a per mg protein basis, their ability to maintain this intracellular Ca++against a low concentration of extracellular Ca++differs markedly. The transformed but not the normal cells rapidly lose Ca++when exposed to low extracellular Ca++, suggesting Ca++transport and/or sequestration differ in the two cell types. In this study we have extended our investigations of Ca++metabolism in the two cell types. We observe that normal WI38 cells, when exposed to metabolic inhibitors to deplete intracellular ATP, undergo a twofold increase in intracellular Ca++levels. Under similar conditions and over the same time course, no comparable change in Ca++level is observed in the SV40‐transformed cell, despite the extensive depletion of ATP.45Ca++desaturation curves indicate that the bulk of the net increase in cell Ca++following ATP depletion of the normal WI38 cell comes to reside in a slowly exchanging Ca++pool. The data also indicate that glycolysis, and not oxidative phosphorylation, drives the active extrusion of Ca++from these cells, an observation consistent with previous studies on the Na+‐K+pump in other cell types. Finally, the data indicate that in these cells mitochondria do not appear to be the major subcellular organelle responsible for regulation of at least the two cellular Ca++pools measurable using isotope desaturation analysis. This is based on the inability of the respiratory inhibitor rotenone to alter significantly the size of either of these Ca++pools. These pools compose 80–90% of total cell Ca++in both cel

ISSN:0021-9541    

DOI:10.1002/jcp.1041200308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractPrevious work from our laboratory has demonstrated that both anticoagulant and nonanticoagulant heparin species can inhibit the proliferation of vascular smooth muscle cells in vivo and in vitro. In this communication, we report studies on the structure‐function relationships of heparin to its antiproliferative effect on vascular smooth muscle cells. These structure‐function studies were carried out by preparing discrete sizes of heparin fragments and by chemically modifying heparin. The compounds were tested for their ability to inhibit rat and calf aortic smooth muscle cell growth. The minimum fragment size which retains some growth inhibitory activity is a hexasaccharide; maximal antiproliferative activity was obtained with dodecasaccharide and larger fragments. Both O‐sulfation and N‐substitution were found to be important for the growth inhibitory effect. Comparison of the antiproliferative and anticoagulant activities of the different heparin species has allowed us to identify several heparin molecules which have lost their anticoagulant properties, but retain antiproliferative a

ISSN:0021-9541    

DOI:10.1002/jcp.1041200309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractThe activity of purine salvage and interconversion enzymes was examined in two sublines of Chinese hamster cells–RA11 and RA41–isolated on the basis of their resistance to adenosine concentrations toxic to wild‐type CCL39 cells. Adenosine deaminase (ADA) activity was found to be two times higher in RA11 and three times higher in RA41 than in CCL39. Inhibition of ADA activity by coformycin reduced the level of adenosine resistance but did not restore wild‐type sensitivity, indicating that a second defect contributes to the adenosine‐resistant phenotype of these variants; evidence was indeed obtained for the presence in both lines of additional alterations protecting them against the lethal depletion of phosphoribosylpyrophosphate (Ishii and Green, 1973) imposed by adenosine to wild‐type cells. To gain better insight into the influence of ADA hyperactivity on adenosine resistance, a procedure was developed for the specific isolation of variants with increased levels of ADA activity. Cell lines with 3–5 times and then 100–500 times the wild‐type ADA activity were stepwise recovered. These investigations confirmed that amplification of ADA can efficiently contribute in protecting cells against high concentrations of exogenous adenosine. The variants isolated by this procedure again manifested, in addition to amplification of ADA activity, another alteration decreasing their sensitivity to adenosine. A possible mechanism accounting for the frequent isolation of variants that coexpress ADA hyper‐activity and a second defect contributing protection against adenosine toxi

ISSN:0021-9541    

DOI:10.1002/jcp.1041200310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY

摘要:

AbstractChinese hamster ovary (CHO) fibroblasts adhere to the extracellular matrix by both fibronectin‐dependent and ‐independent mechanisms (Harper and Juliano, 1981a,b). Previous studies have suggested that a trypsin‐sensitive, 265,000‐dalton membrane glycoprotein (gp265) is involved in the fibronectin‐independent adhesion process. Using a polyclonal antibody against soluble products obtained from trypsin‐treated CHO cells, we have been able to further analyze this involvement. This antibody immunoprecipitates a trypsin‐sensitive 265,000‐dalton protein from detergent‐solubilized cells. Incubation of AdvF11, a variant cell line that does not utilize fibronectin for adhesion, with this antibody blocks their adhesion to extracellular matrix material (ECM). The immunoglobulin fraction will also partially block adhesion of the parental cell line to ECM particularly when the ECM is first treated with an antifibronectin antibody. Taken together these results add support for the involvement of gp265 in fibronectin‐independent adhesion and provide a methodology for furth

ISSN:0021-9541    

DOI:10.1002/jcp.1041200311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1984

数据来源: WILEY